Hydrothermal conversion of Y-zeolite using alkaline earth cations

ABSTRACT

Hydrothermal synthesis of the natural, alkaline earth zeolites via the alteration of Y-zeolite is presented. Synthetic versions of the zeolites harmotome, heulandite, brewsterite and gmelinite are synthesized from Y-zeolite using alkaline earth cations containing solutions. The effect of the composition of the starting zeolite, the composition of the solution phase, the presence or absence of seeds and the experimental conditions are discussed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.08/836,966, filed Jul. 29, 1997 and entitled SYNTHESIS OF ZEOLITES BYHYDROTHERMAL REACTION OF ZEOLITE P1, now U.S. Pat. No. 5,935,551, whichis a nonprovisional application claiming priority to provisionalapplication U.S. Application Ser. No. 60/006,778 filed Nov. 15, 1995,both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for synthesizing zeolites fromY-zeolite. More particularly, the present invention relates to methodsfor synthesizing synthetic analogues of heulandite, brewsterite,epistilbite, harmotome and gmelinite zeolites containing alkaline earthcations using Y-zeolite as a starting material

2. Description of the Related Art

Ever since Barrer's pioneering work (Barrer, et al., J. Chem. Soc.,(1961), 971), numerous studies in zeolite synthesis have concentrated onthe use of organic structure-directing agents (SDAs) in the synthesismixture that affect the crystallization of zeolite. Debate continues onthe roles of various types of organic components in the crystallizationprocess.

One problem with using organic reagents in zeolite synthesis is theircost. In order to reduce the expense of zeolite production, synthesesthat do not use SDAs are desirable. Many natural zeolites that haveunique structures have not been synthesized. Thus, new routes tosynthesize known active zeolites without organic reagents could providelow cost materials Syntheses of the heulandite (HEU) family of zeolites,the most abundant zeolites found in nature, through a number of routeshave been reported by Satokawa, et al. Microporous Mater., 8 (1997), 49;Williams, Chem. Commun., (1997), 2113; Zhao, et al., Zeolites, 19(1997), 366-369; and Zhao, et al., Microporous Mater., 21 (1998),371-379. These syntheses involve conventional hydrothermalcrystallization using alkaline metal cations and amorphous oxides (notzeolites).

Most natural zeolites have alkaline earth cations as the dominant cation(i.e., highest concentration relative to all other metal cationspresent) in their composition. Because of this fact, we studied use ofalkaline earth cations to prepare HEU, harmotome (PHI), brewsterite(BRE), epistilbite (EPI) and Yugawaralite (YUG) type zeolites fromeither zeolite P or L, as reported in Khodabandeh, et al., MicroporousMater. 12:(4-6) 347-359 (December 1997) Khodabandeh, et al., MicroporousMater., 11:(1-2) 87-95 (August 1997), Khodabandeh, et al., MicroporousMater., 9: (3-4) 149-160 (September 1997), Khodabandeh, et al., Chem.Comm., (10) 1205-1206 (May 1996). Of importance to our syntheticmethodology is the starting material, e.g., the ratio of Si/Al andframework density. Hydrothermal conversions without organic SDAs can beeffected only by converting a zeolite with a relatively lower frameworkdensity to one of a relatively higher framework density. Table 1 listsframework density for several zeolites.

TABLE 1 Exemplary Framework Densities Zeolite Framework Density FAU(Y-zeolite) 12.7 GME 14.6 *BEA (zeolite beta) 15.0 GIS (P-zeolite) 15.4BOG 15.6 PHI 15.8 LTL (L-Zeolite) 16.4 HEU 17.0 BRE 17.5 EPI 18.0 YUG18.3

The choice of the starting material for zeolite synthesis with alkalineearth cations is of critical importance.

In 1960, Koizumi and Roy reported synthesis of a heulandite-type zeolitefrom the composition CaO.Al₂O₃ .7SiO₂.5H₂O at temperatures between 250°C. and 360° C. and a pressure range of 15,000 to 37,000 psi. In 1981,Wirsching obtained heulandite by hydrothermal alteration of rhyoliticglass under the action of CaCl₂ solutions at temperatures of 200° C. to250° C. and reaction times of around 80 days. Additionally, somesyntheses for clinoptilolite zeolites have been reported.

Without methods described herein or others developed by one of theinventors, it is either difficult or impossible to produce otherzeolites synthetically. For example, gmelinite cannot be synthesizedfrom zeolite P or L because the framework density gmelinite isrelatively lower than that of either zeolite P or L.

Harmotome, another rare zeolite of hydrothermal origin which has thephillipsite (PHI) topology, is characterized by three dimensionalchannels consisting of pores composed of eight tetrahedral atoms. Thedominant cation in the zeolite is Ba.

Epistilbite, another rare zeolite of hydrothermal origin, has previouslybeen produced by hydrothermal treatment of rhyolytic glass at 250° C.and from powdered SiO₂ glass at 250° C. It has a structure characterizedby intersecting channels composed of eight and ten tetrahedral atoms.

Zeolite beta (*BEA) (occurs naturally as mineral Tschernichite) andBoggsite (BOG) each can be synthesized from Y zeolite according to themethods of the present invention. Tschernichite has a Si/Al of about 5,but this ratio has not been synthesized Boggsite has Si/Al of about 5,but as far as the inventors are aware, has not yet been synthesized.

Since the naturally occurring materials are rare, but so potentiallyuseful, it would be advantageous to enable less rigorous and thereforeless expensive routes for producing greater quantities of thesematerials. Particularly of interest are routes that can producematerials with few or no impurities, i.e., anything other than thedesired zeolite product (e.g., other zeolite by-product).

Y-zeolite (FAU) has long been used as an industrial catalyst due to itshigh activity and low cost. Furthermore, Y-zeolite can be used as analuminum source for ZSM-5 synthesis (e.g., as reported by Bourgogne, etal., U.S. Pat. No. 4,503,024) and to prepare novel materials such aszeolite beta with low Si/Al ratios (Zones, et al., U.S. Pat. No.5,340,563). When Y-zeolice can be used as an aluminum source in zeolitesynthesis, the type of cations for ion exchange is very important. Forexample, although relative to the control (Na—Y), Co—Y or Cu—Y reactionrates to chabazite were just as fast, Fe and Cr inhibit this reactioncompletely, as reported by Zones, J. Chem. Soc. Farad. Trans., 86(1990), 3467 and 87 (1991), 3709 and Stud. Sur. Sci. Catal. Vol. 97, pp.45-52 (1995).

Here, we focus on the use of Y-zeolite as a starting material forhydrothermal conversion with alkaline earth cations. Exemplaryconversions of Y-zeolite to analcime (ANA) and synthetic analogues ofheulandite, gmelinite (GME), harmotome and brewsterite zeolites arepresented. The factors that determine the products are shown to be theSi/Al ratio in the starting zeolite, the presence or absence of seeds,the composition of the reaction medium, and the reaction time.

As one of ordinary skill would recognize, syntheses of other zeolitesfrom Y-zeolite of relatively higher Si/Al, i.e., greater than 3.5, canutilize a commercially prepared Y-zeolite or can be synthesized, as istaught in the literature.

SUMMARY OF THE INVENTION

The present invention provides synthetic routes to form zeolites usingY-zeolite as a starting material. In one aspect, methods according tothe invention use an alkaline earth cation in a hydrothermal alterationof Y-zeolite. In another aspect, methods according to the invention usea second alkaline earth cation in a hydrothermal alteration ofY-zeolite.

The new routes significantly reduce the time necessary to produce thedesired product, and in some cases, permit synthesis of materials forwhich none has yet been previously reported by others, as far as theinventors are aware.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be better understood by reference to thedrawings in which:

FIG. 1 shows ²⁹Si NMR spectra of Y-zeolite as a function of frameworkSi/Al ratio;

FIGS. 2a and 2 b show XRD patterns for synthetic harmotome and syntheticanalcime, respectively, prepared according to the present invention;

FIGS. 3a, 3 b and 3 c show XRD patterns for CIT-3, CIT-4 and syntheticgmelinite, respectively, prepared according to the present invention;

FIG. 4 graphically summarizes zeolite products achieved by treatingY-zeolite according to the present invention;

FIGS. 5a, 5 b and 5 c show XRD patterns of gmelinite, mixtures ofgmelinite and layered phase, respectively; and

FIGS. 6a, 6 b and 6 c show ²⁹Si NMR spectra of gmelinite, mixtures ofgmelinite and layered phase, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention are now described, in which ageneral method for the production of alkaline earth cation-containingzeolites from Y-zeolite is used.

The invention will be better understood by reference to the followingdefinitions. Since naturally occurring zeolites have different namesaccording to their structures and compositions, clarity is needed whenreferring to zeolites.

By “zeolites,” we mean microporous crystalline aluminosilicates as arecommonly known throughout the literature. We refer to zeolites by thenames recognized as indicating their framework topologies and theirchemical compositions. The relevant framework topologies are defined inthe Atlas of Zeolite Structure Types, published by Butterworth-Heinemannfor the structure commission of the International Zeolite Association(IZA), third edition (Meier and Olsen editors), which is incorporatedherein by reference.

By the term “dominant” as used herein, we mean an alkaline earth cationhaving largest content relative to all other metal cations present. Inthe zeolite or reaction medium, the content of all other metal cationsis preferably less than about 1%.

CIT-3 is a synthetic analogue of the natural calcium form of heulanditezeolite. This material typically crystallizes with a composition ofCaO:Al₂O₃:7SiO₂:6H₂O and has a two-dimensional pore system defined byintersecting 8- and 10-member ring pores.

CIT-4 is the first analogue of the rare natural zeolite brewsterite. Ithas a composition of SrO:Al₂O₃:5.8SiO₂:4.5H₂O and possesses thebrewsterite topology, which consists of intersecting 8-member ring poresin two dimensions.

Gmelinite is a natural sodium-calcium zeolite with a typical compositionof 8Na₂O:4CaO:Al₂O₃:4SiO₂:6H₂O. The main 12-member ring channels areinterconnected at right angles by two-dimensional system of 8-memberring channels, and thus form a three-dimensional channel system.

Harmotome is the Ba-dominant analogue of the zeolite phillipsite(Gottardi, et al., Natural Zeolites, Springer-Verlag, Heidelberg(1985)). It has a typical composition of BaO:Al₂O₃:6SiO₂:6H₂O and thephillipsite topology, which consists of 8-member ring channels in threecrystallographic directions.

Analcime is a sodium containing zeolite, with a typical compositionNa₂O:Al₂O₃:4 SiO₂:H₂O and has irregular channels formed by highlydistorted 8-membered rings.

Zeolite Y is the sodium aluminosilicate analogue of the naturalfaujasite possessing three-dimensional 12-membered ring pores The Si/Alratio of the Y-zeolite useful in the methods of the present invention isat least 2.0, preferably between 2.0 and 10.0, more preferably between2.0 and 5.0 and most preferably between 2.0 and 3.5.

Exemplary Syntheses and Analyses:

EXAMPLE 1

Zeolite-Y Starting Materials

Exemplary zeolite Y starting materials prepared were Na—Y zeolites withSi/Al ratios from 2.0 to 3.5. For example, Na—Y zeolite with Si/Al=2.0was prepared in a TEFLON jar by adding 12.0 g of colloidal SiO₂ (LUDOXHS-30) to a stirred solution containing 2.2 g of 50% w/w solution ofNaOH and 1.7 g of sodium aluminate (Na₂O:Al₂O₃:3H₂O, EM) in 13.0 ml ofwater. This mixture was stirred at room temperature for 20-24 hours. Theresulting gel was transferred to a TEFLON-lined stainless steelautoclave and heated at 120° C. for 12 hours under autogenous pressure.After cooling the mixture, the zeolite synthesized was filtered anddried For the synthesis of Na—Y zeolites with Si/Al up to 5, 15-crown-5(i.e., 1,4,7,10,13-pentaoxacyclopentadecane) was added first to thestirred solution. For example, Y-zeolite with Si/Al of 3.5 was preparedas follows: 1.4 g of sodium aluminate were added to a solutioncontaining 1.8 g of 15-crown-5 and 1.8 g of 50% w/w NaOH in 10.0 gwater. 16.0 g of colloidal silica were then added and the mixturestirred at room temperature for 20-24 hours. The resulting reactionmixture was transferred to a TEFLON-lined autoclave reactor andstatically heated at a temperature of 110° C. for 7 days.

For Si/Al greater than about 5, other synthetic routes are known or theY-zeolite can be purchased commercially.

Ion exchange of zeolites was carried out (1 g zeolite/100 mL solution)using 1.0N chloride solutions of the desired cation at 70-80° C.overnight (performed twice). Other solutions of the desired cation maybe used, for example, nitrate or acetate. Carbonate solutions do notwork due to low solubility in water. Thus, the method of the inventionis not limited to use of chloride solutions.

The hydrothermal reaction of Y-zeolite with chloride solutions of thedesired alkaline earth metal cation(s) and seeds, if used, at atemperature of 240° C. (in TEFLON-lined autoclave) was accomplished overthe course of 7 to 24 days. The pH of each solution was adjusted byadding a small amount of a concentrated hydroxide solution of thedesired alkaline earth cation. Seeds, when used, were naturalbrewsterite from Strontian, Scotland and natural heulandite from nearPoona, India. The synthesized products CIT-3 or CIT-4 were also used asseeds instead of natural brewsterite or heulandite.

X-ray powder diffraction patterns were recorded on a Scintag XDS 2000diffractometer using Cu—Kα radiation. The diffracted beam was detectedby a liquid nitrogen-cooled germanium solid-state detector. In the caseof routine analysis and identification of phases., the samples wereanalyzed in the 2θ range 2-51 in steps of 0.03° under a scan speed of5.0°/min. The XRD profile was deconvoluted using split-Pearson lineshapes and the cell parameters were refined using the Scintag cellrefinement program.

Thermogravimetric analyses (TGA) were carried out on a DuPont 951thermogravimetric analyzer. The samples were heated in air and thetemperature ramp was 10° C./min.

Solid-state NMR spectroscopy was performed on a Bruker AM 300spectrometer equipped with solids accessories. Samples were packed into7-mm ZrO₂ rotors and spun in air. ²⁹Si (59.63 Mhz) NMR spectra wereobtained using magic-angle spinning (MAS) at spinning rates of 3-4 kHz,pulse widths of 4s (400 pulse), and recycle delay times of 30-60seconds. Tetrakis (trimethylsilyl) silane (TMS) was used as the externalreference material for ²⁹Si NMR chemical shift determination, and allchemical shifts are reported in ppm relative to TMS. No line broadeningwas applied to the NMR data, Spectral deconvolution and simulation wasperformed using both the Bruker Linesim and MacFID software packages.

Nitrogen adsorption isotherms were collected at −196° C. on an Omnisorp100CX analyzer. Samples were pretreated at 250° C. for 5 hours undervacuum. The adsorption isotherms for vapor-phase compounds were measuredat 25° C. using a McBain-Bakr balance. The adsorption amount of vaporphase compounds was measured at a pressure of P/P₀=0.3. Prior to theadsorption experiments, the samples were dehydrated at 250° C. undervacuum for 5 hours.

Elemental analysis (ICP-MS) was performed by Galbraith Laboratories(Knoxville, Tenn.).

XRD Patterns and NMR Spectra of Y-zeolites

The XRD patterns for all the Y-zeolites in this study revealed that thesamples to be used as starting materials were pure, single phases.

The ²⁹Si NMR spectra for four Y-zeolite samples with Si/Al varying from2.0 to 3.5 are shown in FIG. 1. The four NMR peaks in each spectrumobserved correspond to the following environments in the direction ofdecreasing chemical shift: Si(3Al), Si(2Al), S(1Al) and Si(0Al.).Assuming a random distribution of aluminum in the framework, it ispossible to calculate the framework Si/Al ratio according to theequation:${{Si}/{Al}} = \frac{\sum\limits_{n = 0}^{4}\quad I_{{Si}{({nAl})}}}{\sum\limits_{n = 0}^{4}\quad {\frac{n}{4}I_{{Si}{({nAl})}}}}$

where the intensities of the peaks corresponding to Si(0Al) throughSi(4Al) are determined by simulating the NMR spectrum. ²⁹Si NMRspectroscopy was used to determine the true framework Si/Al ratio of allY-zeolites used in our experiments, and the values reported in FIG. 2and in the text and tables are obtained via this method.

Conversions of Y-zeolite

Y-zeolites that have been synthesized with framework Si/Al ratiosbetween 2.0 and 3.5 are used as the starting materials for methodsaccording to the present invention. The conversion of these materials toother zeolites in solutions in which any of Ba²⁺, Ca²⁺, Na⁺, and Sr²⁺ isdominant is described below.

EXAMPLE 2

Y-zeollte in a barium-dominant reaction medium

In a barium-dominant aqueous reaction medium, harmotome (PHI) was theonly product obtained at all conditions through the hydrothermalconversion from Y-zeolite (see Table 2). These reactions were performedusing Y-zeolite with Si/Al ratio between 2.0 and 3.5, and a solutionphase (reaction mixture) of BaCl₂ at a concentration of 0.1N andpH=11-12 (adjusted by the addition of Ba(OH)₂). The XRD pattern of thesynthetic harmotome zeolite product obtained is shown in FIG. 2a. In thepresence of seeds of heulandite or brewsterite, the product of thereaction is still harmotome. Seeding is usually at least about 1%; andtypically 1-10%.

TABLE 2 Reactions to Y-zeolite with barium-containing solutions^(a)Starting phase Si/Al^(b) pH^(c,d) Seeds Result Sr-Y 2.0 11 — PHI Sr-Y2.4 11 — PHI Sr-Y 3.0 11 — PHI Sr-Y 3.0 11 BRE (5%) PHI Sr-Y 3.0 11 HEU(5%) PHI Sr-Y 3.5 11 — PHI Ca-Y 3.0 11 — PHI ¹0.02 g of Y-zeolite wasreacted with 10 ml to solution phase at 240° C. ^(b)Si/Al ratio wasdetermined from ²⁹Si NMR data. ^(c)Ph was adjusted by the addition of afew drops of Ba(OH)₂ solution. ^(d)[Ba²⁺] = 0.1 N.

EXAMPLE 3

Y-zeolite in a calcium-dominant reaction medium

In a calcium-dominant aqueous reaction medium under conditionsexemplified in Example 2, no hydrothermal conversion of Y-zeolitesion-exchanged by Ba²⁺, Ca²⁺, and Sr²⁺ occurred even in the presence of5% seeds of appropriate crystals (see Table 3). This result contrastswith the previous study for synthesis CIT-3 and CIT-4 from zeolite P1where transformation takes place with calcium-containing solutions.

TABLE 3 Reactions of Y-zeolite with calcium-containing solutions^(a)Starting phase Si/Al^(b) pH^(c,d) Seeds Result Sr-Y 2.0 11 — FAU Sr-Y2.4 11 — FAU Sr-Y 3.0 12 — FAU Sr-Y 3.0  9 — FAU Sr-Y 3.0 11 BRE (5%)FAU Sr-Y 3.0 11 HEU (5%) FAU Sr-Y 3.5 11 — FAU Ca-Y 3.0 11 — FAU Ca-Y3.0 11 HEU (5%) FAU Sr-Y 3.5 11 — FAU Ba-Y 3.0 12 — FAU ^(a)0.02 g ofY-zeolite was reacted with 10 ml of solution phase at 240° C. ^(b)Si/Alratio was determined from ²⁹Si NMR data. ^(c)pH was adjusted by theaddition of a few drops of Ca(OH)₂ solution. ^(d)[Ca²⁺] = 0.1 N.

EXAMPLE 4

Y-zeolite in a sodium-dominant reaction medium

In a sodium-dominant aqueous reaction medium, the product of conversionof NaY-zeolite that has Si/Al ratio from 2.0 to 3.0 was analcime (ANA)(see Table 4). The XRD pattern of this synthetic zeolite is shown inFIG. 2b. By comparison, conversion of Sr—Y in sodium-dominant aqueousreaction medium yielded analcime and gmelinite.

TABLE 4 Reactions of Y-zeolite with sodium-containing solutions^(a)Starting phase Si/Al^(b) pH^(c,d) Seeds Result Na-Y 2.0 12 — ANA Sr-Y2.0 11 — ANA + GME Na-Y 2.4 12 — ANA Sr-Y 2.4 11 — ANA + GME Na-Y 3.0 12— ANA ^(a)0.02 g of Y-zeolite was reacted with 10 ml of solution phaseat 240° C. ^(b)Si/Al ratio was determined from ²⁹Si NMR data. ^(c)pH wasadjusted by the addition of a few drops of NaOH solution. ^(d)[Na⁺] =0.1 N.

EXAMPLE 5

Y-zeolite in a strontium-dominant reaction medium

In a strontium-dominant aqueous reaction medium, three types ofstrontium-containing zeolites were obtained (see Table 5). Y-zeolite wasconverted to brewsterite (CIT-4), Sr-heulandite (CIT-3), and gmelinite.Sr—Y zeolite having a Si/Al ratio of 3.0 was transformed thoroughly intoCIT-3 and CIT-4 in the presence of 5% seeds of the appropriate type. TheXRD patterns of these synthetic zeolites are shown in FIG. 3.

TABLE 5 Reactions of Y zeolite with strontium-containing solutions^(a)Starting phase Si/Al^(b) pH^(c,d) Seeds Result Sr-Y 2.0 11 — GME Sr-Y2.0 11 BRE (5%) GME + CIT-4 Sr-Y 2.0 11 HEU (5%) GME + CIT-3 Sr-Y 2.4 11— GME Sr-Y 2.4 11 BRE (5%) GME + CIT-4 Sr-Y 2.4 11 HEU (5%) GME + CIT-3Sr-Y 3.0 11 — Amorphous Sr-Y 3.0 11 BRE (5%) CIT-4 Sr-Y 3.0 11 HEU (5%)CIT-3 Sr-Y 3.5 11 — Amorphous Sr-Y 3.5 11 BRE (5%) Amorphous Sr-Y 3.5 11HEU (5%) Amorphous Ca-Y 3.0 11 — Ca-Y Ca-Y 3.0 11 BRE (5%) Ca-Y + CIT-4Ca-Y 3.0 11 HEU (5%) Ca-Y + CIT-3 ^(a)0.02 g of Y-zeolite was reactedwith 10 ml of solution phase at 240° C. ^(b)Si/Al ratio was determinedfrom ²⁹Si NMR data. ^(c)pH was adjusted by the addition of a few dropsof Sr(OH)₂ solution. ^(d)[Sr²⁺] = 0.1 N.

The conversion of Sr—Y zeolite to gmelinite occurred with Sr—Y zeolitehaving Si/Al under 2.4 and only in the absence of seeds. It appears thatSr—Y zeolite with low Si/Al ratio was converted to gmelinite because theSi/Al ratio of gmelinite is normally close to 2.0. On the other hand,only amorphous phases were obtained from Sr—Y zeolite with Si/Al ratiosover 3.0 in the absence of seeds.

When Ca—Y zeolite was the starting material after hydrothermalconversion, XRD analysis revealed the XRD pattern of FAU in combinationwith CIT-3 or CIT-4. As shown in Table 5, Sr—Y zeolite having Si/Alratio of 3.5 was not transformed into crystalline phase, even in thepresence of seeds The results presented above show that Y-zeoliteshaving Si/Al in a certain range are particularly useful startingmaterials for the preparation of a number of alkaline earth zeolitesusing methods of the present invention. FIG. 4 summarizes results ofthese conversions of Y-zeolite to other zeolites.

EXAMPLE 6

Effect of experimental conditions on the synthesis of gmelinite

As shown by the data presented above, gmelinite was synthesized fromSr—Y zeolite with Si/Al ratio under 2.4 in a strontium-dominant reactionmedium. Although research of gmellnite synthesis with strontium cationhas been carried out for a long time, reproducibility of qmelinitesynthesis was sometimes nil (Barrer, et al., 86 Hydrothermal Chemistryof Silicates; Part XII, (1964) 485-497). In order to determine thefactors responsible for the lack of reproducibility of this synthesis,great care has been taken by the inventors to standardize factors suchas temperature, heating time (duration in days), pH, solutionconcentration of strontium, and ratio of solution/starting zeolite.Table 6 summarizes the effects of these experimental factors ongmelinite synthesis.

TABLE 6 Reactions of Sr-Y with strontium-containing solutions^(a)Solution Volume Temperature Duration Zeolite [Sr²⁺], N pH^(b) (ml) (°C.) (Days) Product 0.1 7 10 240 14 GME + CHA 0.1 10 10 240 14 GME + CHA0.1 11 10 240 14 GME 0.1 12 10 240 14 GME 0.1 12.5 10 240 14 GME +Layered 0.1 13 10 240 14 GME + Layered 1.0 12 10 240 14 GME + Layered0.1 12  5 240 14 GME + Y-Zeolite 0.1 12 15 240 14 GME + Layered 0.1 1210 200 14 GME + CHA 0.1 10 15 240 14 GME 0.1 10 10 240 21 GME 0.1 12 20240 14 GME + Layered ^(a)0.02 g of Sr-Y zeolite with Si/Al = 2.0 wasreacted with the solution. ^(b)pH was adjusted by the addition of a fewdrops of Sr(OH)₂ solution.

Chabazite (CHA) was synthesized as an impurity with strontium-containingsolutions of lower pH (<10) or at lower temperatures (<200° C.).However, if the hydrothermal conversion was carried out for longduration (>21 days) or with a large amount of the solution (>15 ml),chabazite was not synthesized even at low pH.

Strontium-containing solutions of higher pH (>12.5) induced synthesis oflayered phases (“layered” designation in Table 6). XRD patterns and NMRspectra of structures of gmelinite and layered phases are shown in FIGS.5 and 6, respectively. Layered phases have also been obtained withsolutions of higher strontium concentration (>1.0N) and a large amountsof the solution (>15 ml).

In summary, high pH, relatively high dominant alkaline earth cationconcentration and a large amount of the solution produce chabazite withgmelinite while, low pH, relatively low dominant ion alkaline earthcation concentration and a small amount of the solution give the layeredphase. Chabazite also occurred with short heating duration and lowtemperature, while the layered phase was synthesized at longer times andhigher temperatures.

Adsorption onto gmelinite

Although GME structure has the main 12-membered ring channelsinterconnecting at right angles with a two-dimensional system of8-membered ring channels, only 1.0% cyclohexane was adsorbed onto anatural gmelinite (Na, Ca form) and 7.3% cyclohexane was adsorbed evenon a fault-free gmelinite (Daniels, et al., J. Am. Chem. Soc., (1978),3097). On the other hand, a natural gmelinite (Nova, Scotia) sorbed0.0767 cc/g N₂ at −196° C. (Breck, Zeolite Molecular Sieves (1974) 625).

Gmelinite synthesized from Sr—Y zeolite according to the inventionadsorbs 0.155 cc/g-zeolite N₂ at −196° C. and 0.120 cc/g H₂O, 0.137 cc/gCH₃OH and 0.145 cc/g C₂H₅OH at 25° C. (see Table 7). Propyl alcohols andhexanes are not adsorbed onto this zeolite.

TABLE 7 Adsorption onto synthetic gmelinite^(a) Temperature at Resultscc/g- Adsorbates adsorption zeolite Nitrogen N₂ −196° C.  0.155Cyclohexane C₆H₁₂ 25° C. N.A.^(b) n-hexane C₆H₁₄ 25° C. N.A. i-propylalcohol i C₃H₇OH 25° C. N.A. n-propyl alcohol n C₃H₇OH 25° C. N.A.Ethanol C₂H₅OH 25° C. 0.145 Methanol CH₃OH 25° C. 0.137 Water H₂0 25° C.0.120 ^(a)Samples were treated at 350° C. prior to adsorption. ^(b)N.A.= no adsorption.

As can be seen from Table 7, gmelinite synthesized by hydrothermalconversion of Y-zeolite according to the invention shows higher capacityfor the adsorption (at least of nitrogen) than natural gmelinite.

A number of alkaline earth zeolites have been synthesized throughhydrothermal conversion of Y-zeolite with solutions containing alkalineearth cations according to methods of the present invention. Among thesezeolites are synthetic analogues of the zeolites heulandite,brewsterite, harmotome and gmelinite. The Si/Al ratio of Y-zeolite has asignificant influence on the final zeolites obtained. Barium was asuitable cation for the synthesis of harmotome, calcium was noteffective for the conversion of Y-zeolite, and strontium showed thegreatest variety of behaviors for the hydrothermal conversion ofY-zeolite to synthetic analogues of the natural zeolites. Gmelinitesynthesized from Sr—Y zeolite had adsorption capacities that lie betweenthese of natural (faulted) GME and a reported fault-free GME (Daniels,et al., J. Am. Chem. Soc., (1978) 3097; Breck, Zeolite Molecular Sieves(1974) 625).

While the present invention is disclosed by reference to the preferredembodiments set forth above, it is to be understood that these areintended in an illustrative only. For example, based on the disclosureshere relating to alkaline earth and alkali metal containing zeolites(and their preparation), modifications will readily occur to thoseskilled in the art. Such modifications which relate to these methods arenew zeolites are considered to be within the spirit of the invention andwithin the scope of the appended claims.

We claim:
 1. A method for synthesizing a zeolite, comprising the stepsof: a) providing a Y zeolite having 2.0≦Si/Al≦3.5 and which includes analkaline earth cation; and b) forming said zeolite under hydrothermalreaction conditions from a reaction mixture containing said Y-zeoliteand aqueous solution of an alkaline earth cation.
 2. A method accordingto claim 1, wherein said alkaline earth cation in said Y-zeolite andsaid alkaline earth cation in said reaction mixture are the same.
 3. Amethod according to claim 1, wherein the content of other metal cationsin said reaction mixture is less than 1%.
 4. A method according to claim1, wherein the reaction mixture further contains seeds of a zeolite. 5.A method according to claim 3, wherein said seeds are selected from thegroup consisting of heulandite and brewsterite zeolites.
 6. A methodaccording to claim 1, wherein said zeolite formed is selected from thegroup consisting of heulandite, gmelinite, harmotome, analcime,chabazite and brewsterite and mixtures thereof.
 7. A method according toclaim 1, wherein said alkaline earth cation is selected from the groupconsisting of Ba²⁺, Ca²⁺, and Sr²⁺.
 8. A method for synthesizing azeolite, comprising the steps of: a) providing a Y zeolite having2.0≦Si/Al≦3.5; and b) forming said zeolite under hydrothermal reactionconditions from a reaction mixture containing said Y-zeolite and aqueoussolution of an alkaline earth cation, the reaction mixture beingsubstantially free of any zeolite directing agent.
 9. A method forpreparing synthetic heulandite, gmelinite, brewsterite, analcime orharmotome zeolite product, comprising the steps of: a) providing areaction mixture containing Y-zeolite having 2.0≦Si/Al≦3.5 and analkaline earth cation, wherein the alkaline earth cation is in aconcentration greater than that of the concentration of any other metalcation present in the reaction mixture; and b) converting underhydrothermal conditions said Y-zeolite in said reaction mixture to saidzeolite product containing said alkaline earth cation.
 10. A methodaccording to claim 9, wherein said Y-zeolite includes an alkaline earthcation.
 11. A method according to claim 10, wherein said alkaline earthcation in said Y-zeolite and said alkaline earth cation in said reactionmixture are the same.
 12. A method according to claim 9, wherein thereaction mixture contains seeds of a zeolite.
 13. A method according toclaim 12, wherein said seeds are selected from the group consisting ofheulandite and brewsterite zeolites.
 14. A method according to claim 10,wherein said alkaline earth cation is selected from the group consistingof Ba²⁺, Ca²⁺ and Sr²⁺.
 15. A method according to claim 9 consisting ofsteps a) and b).
 16. A method according to claim 9, wherein paid zeoliteproduct is a mixture of any of gmelinite, brewsterite, analcime, andharmotome zeolites.
 17. A method for preparing a zeolite having thephillipsite topology and the formula in terms of atomic ratiosBaO:Al₂O₃:6SiO₂:6H₂O, comprising the steps of: a) providing a reactionmixture containing a first alkaline earth cation and a Y-zeolite, saidY-zeolite having 2.0≦Si/Al≦3.5 and a second alkaline earth cation, themixture being substantially free of any other alkaline earth cations andany zeolite structure directing agent; and b) forming said zeolite fromsaid Y-zeolite under hydrothermal reaction conditions, said zeoliteincorporating a first alkaline earth cation into its framework.
 18. Amethod according to claim 17, wherein said first alkaline earth cationis Ba²⁺.
 19. A method according to claim 17, wherein said secondalkaline earth cation is Sr²⁺.
 20. A method according to claim 17,wherein said reaction mixture further contains seeds of a zeoliteselected from the group consisting of heulandite and brewsteritezeolites.
 21. A method for preparing a zeolite having the brewsteritetopology and the formula in terms of atomic ratios SrO:Al₂O₃:5.8SiO₂:4.5 H₂O comprising the steps of: a) providing a reaction mixturecontaining a first alkaline earth cation and a Y-zeolite, said Y-zeolitehaving 2.0≦Si/Al≦3.0 and a second alkaline earth cation, the mixturebeing substantially free of any other alkaline earth cations and anyzeolite structure directing agent; and b) forming said zeolite from saidY-zeolite under hydrothermal reaction conditions, said zeoliteincorporating a first alkaline earth cation into its framework.
 22. Amethod according to claim 21, wherein said first alkaline earth cationis Sr²⁺.
 23. A method according to claim 21, wherein said secondalkaline earth cation is Sr²⁺.
 24. A method according to claim 21,wherein said reaction mixture further contains seeds of heulanditezeolite.
 25. A method for preparing a zeolite having the heulanditetopology comprising the steps of: a) providing a reaction mixturecontaining a first alkaline earth cation and a Y-zeolite, said Y-zeolitehaving 2.0≦Si/Al≦3.0 and a second alkaline earth cation, the mixturebeing substantially free of any other alkaline earth cations and anyzeolite structure directing agent; and b) forming said zeolite from saidY-zeolite under hydrothermal reaction conditions, said zeoliteincorporating a first alkaline earth cation into its framework.
 26. Amethod according to claim 25, wherein said first alkaline earth cationis Sr²⁺.
 27. A method according to claim 25, wherein said secondalkaline earth cation is Sr²⁺.
 28. A method according to claim 25,wherein said reaction mixture further contains seeds of heulanditezeolite.
 29. A method for preparing a zeolite having the gmelinitetopology comprising the steps of: a) providing a reaction mixturecontaining a first alkaline earth cation and a Y-zeolite, said Y-zeolitehaving 2.0≦Si/Al≦2.4 and a second alkaline earth cation, the mixturebeing substantially free of any other alkaline earth cations and anyzeolite structure directing agent; and b) forming said zeolite from saidY-zeolite under hydrothermal reaction conditions, said zeoliteincorporating a first alkaline earth cation into its framework.
 30. Amethod according to claim 29, wherein said first alkaline earth cationis Sr²⁺.
 31. A method according to claim 30, wherein said secondalkaline earth cation is Sr²⁺.